It is desirable that a sprinkler, or a sprinkler system, water only that area which is intended to be watered. Watering outside of the intended area not only wastes water, but can have other undesirable consequences if the water falls on areas or objects which are not intended to be watered. For example, if a sprinkler sprays water against the side of a house, this can lead to premature degradation of paint applied to the house. Likewise, if a sprinkler sprays water in an area which is not intended to be irrigated, this can promote weed growth in the unintended area.
By and large, most sprinkler heads intended for the irrigation of lawns and the like are configured to sprinkle in a circular pattern, or at least a pattern circumscribing a circular arc. For example, in-ground sprinkler systems utilize one or both of pop-up spray heads and/or rotary spray heads, both of which are typically limited to spraying in circular (or circular arc) spray patterns. Likewise, many free-standing moveable lawn sprinklers are also limited to spraying in circles or circular arcs.
Most in-ground water sprinkler systems employing pop-up spray heads and/or rotary spray heads are configured with the sprinkler heads positioned at corners or edges of the intended area to be watered. This facilitates (but does not ensure) watering the intended area, since the spray from the sprinkler heads is directed inward of the perimeter of the intended area. For example, for a square area intended to be watered (such as a common residential lawn or yard), a typical in-ground sprinkler system may include two sprinkler heads positioned at opposing corners of the yard. In this case only the intended area to be sprinkled will most likely be watered, yet there will be a region of overlap concentrated towards the center of the yard. Thus, the area is not evenly irrigated, and edge areas will typically become dry sooner, while the central area may remain quite moist (thus promoting grown of fungus and the like in this area). This situation is depicted in FIG. 1A, which shows a plan view of an area A1 which is desired to be watered (or irrigated). In the example depicted in FIG. 1A, the area A1 to be watered is bounded by border 1, and is depicted as generally being a square area. In this example two sprinkler heads, 10′ and 10″, are located at opposite corners of the square area A1. Each of the sprinkler heads 10′ and 10″ are configured to provide spray over an area consisting of a circular arc of 90 degrees. Thus, sprinkler head 10′ will cover an area bounded by the upper edge A1-1, the left-most edge A1-2, and the arc 4, while sprinkler head 10″ will cover an area bounded by the lower edge A1-3, the right-most edge A1-4, and the arc 5. As can be seen, this will result in an area 3 of overlapping spray, thus providing essentially twice as must water to area 3 as to areas 2. As can be appreciated, this is an undesirable situation, since water is not evenly applied to areas 2 and 3.
Alternately, if a sprinkler head which sprays in a circular pattern is placed inward of the perimeter of a square lawn area, its circular pattern will miss corner areas, and will typically insufficiently irrigate edge areas. That is, a sprinkler head configured to provide a circular spray pattern will inherently be incapable of sprinkling an area which is not bounded by a circular perimeter. Since most lawns, yards and gardens are non-circular in shape, the common pop-up and rotary sprinkler spray heads cannot water such areas without either (1) spraying beyond the perimeter of the intended area, or (2) depriving parts of the intended area to be watered from receiving the desired quantity of water. This is graphically depicted in FIG. 1B, which shows a plan view of the area A1 (of FIG. 1A) which is desired to be watered (or irrigated). In this instance, a single rotary sprinkler head 10 is centrally located in the essentially square area A1 which is to be sprinkled. As can be seen, a water flow from sprinkler 10 which covers the entire area A1 (bounded by circle 7) also includes overspray of areas 9, which can result in (1) waste of water, and (2) undesirable application of water to features (such as housing siding and the like) located in areas 9. On the other hand, a water flow from sprinkler 10 which does not provide overspray into areas 9 will be bounded by circle 6, but will not provide water to corner areas 8.
The problem depicted in FIGS. 1A and 1B becomes more acute when the area to be sprinkled is of a complex geometry. FIG. 1C is a plan view of an area A2 to be sprinkled which includes a number of different geometric shapes (e.g., concave edges, convex edges, straight edges, and non-parallel edges). The area A2 to be sprinkled is defined by a perimeter line “PL2” (which is not necessarily straight, curved, and/or continuous). A prior-art solution to the problem of watering the area A2 of FIG. 1C is depicted in FIG. 1D. In FIG. 1D, four separate sprinkler placements (10A, 10B, 10C and 10D) are provided to generally cover the area A2. (The four separate sprinkler placements can either be provided by a fixed in-ground sprinkler system, or by systematically placing a single sprinkler in each of the four indicate positions). In the example of FIG. 1D, sprinkler heads 10A and 10C are rotating sprinkler heads, configured to sprinkle over areas bounded by perimeters 20 (in the case of sprinkler 10A), and 24 (in the case of sprinkler 10C). Also in the example of FIG. 1D, sprinkler heads 10B and 10B are rotating sprinkler heads (or, alternately, pop-up circular spray pattern sprinkler heads) bounded by respective perimeters 22 (for sprinkler head 10B) and 26 (for sprinkler head 10D). As can be seen from FIG. 1D, the proposed pattern of sprinkler head placement (for sprinkler heads 10A, 10B, 10C and 10D) provides overspray (i.e., irrigation to non-desired areas) in areas 28, overlapping watering in other areas (30), and no watering to area 32. Further, as can be appreciated from FIG. 1D, the proposed watering arrangement requires either the placement of four separate in-ground sprinkler heads (10A, 10B, 10C and 10D), or four separate placements by a user of a single sprinkler head over a period of time to achieve the indicated coverage. In the first instance (i.e., placement of four separate in-ground sprinkler heads), this increases cost and complexity of an in-ground sprinkler system. In the second instance (i.e., four separate placements of a single sprinkler by a user over a period of time), this requires increased user involvement, which may be undesirable to the user.
Some proposed solutions to this problem are known in the prior art. For example, U.S. Pat. No. 1,796,942 describes a rotating sprinkler head which can vary the distance from the sprinkler head to the outer reach of the spray pattern by adjusting the angle of declination of the sprinkler head. This is done by using fixed cams which cause the sprinkler head to selectively move angularly up-and-down through the cycle of rotation. As is apparent, a separate cam is required for each spray area. That is, the sprinkler head is not “programmable” other than by replacing one cam with another.
Another proposed prior art solution to the problem described above can be found in U.S. Pat. No. 3,528,093. The '093 patent describes a rotating sprinkler head which can vary the distance from the sprinkler head to the outer reach of the spray pattern by adjusting the volumetric flow of water to the sprinkler head. This is accomplished by using a cam which throttles flow as a function of position of the sprinkler head through the cycle of rotation. As with the device described in the '942 patent, a separate cam is required for each spray area.